After a great deal of research, measuring and head scratching I finally settled on Mazda B2200 utility lower ball joints for the lower wishbone ball joint. They had to be mounted upside down to suit the original position on the MX5 upright. They did not fit straight in, and the uprights would require machining, but they were the most suitable that I could find. These were my solution but I am sure other Locost builders will come up with other alternatives.
